1. Field of the Invention
The present invention relates to a color combining optical system (color separating-combining optical system). More particularly, the present invention relates to a color combining optical system for use in an image projection apparatus, such as a liquid-crystal projector, and to an image projection apparatus.
2. Description of the Related Art
U.S. Pat. No. 6,626,540 discusses a color separating-combining optical system for use in a reflective liquid-crystal projector, in which a dichroic mirror and three polarizing beam splitters (PBSs) are located on an optical path between an illumination optical system and a projection optical system. However, the number of components of the color separating-combining optical system is large. Further miniaturization of the color separating-combining optical system is required.
Japanese Patent Application Laid-Open No. 2003-021807 discusses a liquid-crystal projector configured with one PBS and one dichroic prism. Consequently, miniaturization of a liquid-crystal projector is achieved.
However, in the liquid-crystal projector discussed in Japanese Patent Application Laid-Open No. 2003-021807, image light reflected from a liquid crystal panel passes through a dichroic prism before being analyzed by the PBS. Thus, a polarization state of image light immediately after being reflected from the liquid crystal panel is changed by the image light passing through the dichroic prism. Consequently, contrast of a projected image is reduced.